Patent GB-619518-A (GB)
Title: Improvements in or relating to indicating instruments, such as altimeters
IPC: G01L7/00
Filed: 1946-04-25
Abstract: 619,518. Altimeters ; transfer mechanism ; indicating-apparatus. BENDIX AVIATION CORPORATION. April 25, 1946, No. 12512. Convention date, April 27, 1945. [Classes 106 (i), 106 (ii) and 106 (iv)] In an altimeter or the like having a number of pointers separately driven from a drive shaft at different speed ratios to indicate altitude on a scale, there is provided means for setting the pointers independently of the actuator means comprising a differential gear train inserted between the drive shaft and the actuator means and manually operable means for actuating this gear train to drive the drive shaft independently of the actuator means. The altimeter comprises an outer casing 25 in which is removably secured a compound frame structure 16, 23 carrying the mechanism. The aneroid 20 actuates, through a bimetal arm 30, a link 28 which is connected through a U-shaped spring 37 to a pin secured to a rock-shaft 31 to rotate the latter against the action of a spiral spring 46. The shaft 31, mounted for adjustment in an eccentric bush, carries a sector gear 41 mating with a pinion 42 on a shaft 43 which is coaxial with a shaft 68 and drives the latter through gears 56, 65 and 66, 67. The gears 65, 66 are secured on a shaft 57 disposed in a gap in, and carried by brackets secured to, a planetary gear 51 which is normally fixed against rotation by a spring friction plate 52. The shaft 68 carries gears 75, 78, 83 meshing respectively with a pinion 77 on a shaft 76 carrying a pointer 86, a gear 81 on a sleeve 82 carrying a pointer 87 and a gear 84 on an outer sleeve 85 carrying a pointer 88, the three pointers moving with relative speeds in the ratio 100: 10: 1 over a scale 89. The scale 89 is cut away at 90 to reveal a lower scale 91 carried by a gear 99. The pointers 86, 87, 88 will normally indicate altitude with respect to standard barometric pressure at sea level, but means are provided for adjusting the pointers to indicate zero when the instrument is on the ground regardless of the altitude of the ground with respect to sea level. This means comprises a vertical shaft projecting beyond the casing and provided with a knob 92 (not shown). A pinion on this shaft mates with one gear of a two-part gear 95 (not shown) which mates respectively with a gear meshing with the large planetary gear 51 and a second gear secured to a shaft 103, Fig. 3. The shaft 103 has secured thereon a gear 102 which meshes with the gear 99 carrying the under scale 91. Rotation of the knob 92 thus adjusts the scale 91 to the desired initial setting; corresponding correction is applied to the reading of the pointers 86, 87, 88 on the top scale since the gear 51 is also rotated to carry with it the shaft 57 on which the gears 65, 66 are mounted. The sector gear 41 prevents rotation of the,gear 56 during this adjustment so that rotation of the gear 67, shaft 68 and pointers is effected relatively to the sector gear 41. Provision is made whereby rotation of the knob 92 adjusts the pointers only. This comprises means for adjusting the two-part gear 95 vertically so that the gear driving the shaft 103 is disengaged from the gear on the latter. Specifications 429,921 and 438,137 are referred to.